<timer> was renamed in open-dylan/master to <profiling-timer>. following through

It seems this won't work at our current release (https://github.com/dylan-lang/opendylan/blob/v2013.2/sources/common-dylan/timers.dylan#L7), the rename is active on master though (https://github.com/dylan-lang/opendylan/blob/master/sources/common-dylan/timers.dylan#L7);

this fixes issue https://github.com/dylan-foundry/tracing/issues/12